refactor: Extract performance logging to separate class (#124)

This should not be responsibility of LLMClientInterface. Extracting this
class also adds flexibility to silence logging output in tests.

logger/CMakeLists.txt

@@ -1,6 +1,9 @@
 add_library(QodeAssistLogger STATIC
+    EmptyRequestPerformanceLogger.hpp
+    IRequestPerformanceLogger.hpp
     Logger.cpp
     Logger.hpp
+    RequestPerformanceLogger.hpp RequestPerformanceLogger.cpp
 )
 
 target_link_libraries(QodeAssistLogger